<!DOCTYPE html>
<html>
<style>
iframe {
    display: block;
    border: 1px solid black;
    width: 500px;
    height: 300px;
    margin-left: 10px;
    margin-top: 0px;
}
</style>
<body>
<iframe src="data:text/html,Hello%20world"></iframe>
</body>
</html>

